1. Field of the Invention
The present invention relates to a paper feeder assembly for an image forming apparatus such as copying machines or printers, and to an image forming apparatus which incorporates the paper feeder assembly.
2. Description of the Related Art
Paper feeder assemblies for an image forming apparatus are generally configured to allow a roller, such as a rubber roller whose surface is formed of an elastic material, and a pressing member to sandwich a sheet of paper therebetween to rotate it, thereby feeding the sheet.
However, when such a roller of an elastic material is kept out of use for a long time, the roller is held in pressurized contact with the pressing member with the elastic material left in a deformed state. This may cause the elastic material to be permanently deformed. This problematic phenomenon can occur to any rollers depending on their conditions so long as they are made of an elastic material. In particular, the elastic material of a fixing unit is often designed to deform to a large extent. In addition, the roller in the fixing unit is repeatedly heated and cooled, and can be kept permanently deformed with a high possibility. When the deformation becomes permanent, the roller does not rotate smoothly, thereby raising several problems. For example, the deformation causes a change in paper feed speed only at the deformed portion and deterioration in image quality solely at the deformed portion. A variation in torque at the deformed portion can cause the drive portion or structured portion to vibrate, resulting in unusual noise being produced.
These problems were attempted to be solved by a mechanism for automatically varying the applied force of the roller and the pressing member using a pressing unit, a cam, and a drive unit for rotating the cam (for example, as suggested in Japanese Patent Application Laid-open No. 2007-271917). However, such a method requires a driving source for driving the cam and a mechanism for transmitting the drive power, leading to an increase in size and costs of the whole unit. Furthermore, this method requires electric power to relieve the applied force. This may cause the pressurized contact to remain unreleased when the user has cut off the power source before the image forming apparatus stops operating completely. This could lead to the aforementioned problems.
Another exemplary attempt for solving the aforementioned problems was to employ a pressurized-contact release mechanism as disclosed in Japanese Patent Application Laid-open No. 2009-122562. However, this mechanism should be manually operated. And, based on the common sense, it cannot be said that the user always operates this mechanism without fail before leaving the apparatus unused for a long period of time.
It is therefore an object of the present invention to provide a paper feeder assembly for an image forming apparatus which is capable of preventing the deformation of a roller made of an elastic material. It is another object of the invention to provide an image forming apparatus which incorporates this paper feeder assembly.